The significance of partial migration for food web and ecosystem dynamics

Migration is ubiquitous and can strongly shape food webs and ecosystems. Less familiar, however, is that the majority of life cycle, seasonal and diel migrations in nature are partial migrations: only a fraction of the population migrates while the other individuals remain in their resident ecosystem. Here, we demonstrate different impacts of partial migration rendering it fundamental to our understanding of the significance of migration for food web and ecosystem dynamics. First, partial migration affects the spatiotemporal distribution of individuals and the food web and ecosystem-level processes they drive differently than expected under full migration. Second, whether an individual migrates or not is regularly correlated with morphological, physiological, and/or behavioural traits that shape its food-web and ecosystem-level impacts. Third, food web and ecosystem dynamics can drive the fraction of the population migrating, enabling the potential for feedbacks between the causes and consequences of migration within and across ecosystems. These impacts, individually and in combination, can yield unintuitive effects of migration and drive the dynamics, diversity and functions of ecosystems. By presenting the first full integration of partial migration and trophic (meta-)community and (meta-)ecosystem ecology, we provide a roadmap for studying how migration affects and is affected by ecosystem dynamics in a changing world.     

Role of fungal patchiness on vegetal detritus in the trophic interactions between two brackish detritivores,Idotea baltica and Gammarus insensibilis

We investigated patterns of resource partitioning between two brackish crustaceans (I. baltica and G. insensibilis) on trophic mosaics of fungal species colonizing vegetal detritus. Laboratory feeding experiments were carried out to assess consumption rates and diet selection of single individuals belonging to five populations. Adults of two co-occurring population of both G. insensibilis and I. baltica and one population of G. insensibilis, occurring alone in another habitat patch, were studied. Each individual were offered both fragments of Cymodocea nodosa conditioned by 8 fungal species and sterilized fragments as sole food source for 7 days. Both species preferred "conditioned" detritus but potential resource use was greater in G. insensibilis than in I. baltica. Individual niche breadth increased and phenotypic variability reduced in the allotopic sample. Trophic similarities were lower between individuals of co-occuring populations than between I. baltica and the allotopic G. insensibilis. The results suggest that co-occurrence is an important factor contributing to the enhancement of phenotypic variability and, consequently, to a trophic generalization at population level in G. insensibilis. It emphasizes the role of fungal patchiness on detritus in regulating resource partitioning between the two species.     

Swimming with the giant: coexistence patterns of a new redfin minnow Pseudobarbus skeltoni from a global biodiversity hot spot

Ecological niche theory predicts that coexistence is facilitated by resource partitioning mechanisms that are influenced by abiotic and biotic interactions. Alternative hypotheses suggest that under certain conditions, species may become phenotypically similar and functionally equivalent, which invokes the possibility of other mechanisms, such as habitat filtering processes. To test these hypotheses, we examined the coexistence of the giant redfin Pseudobarbus skeltoni, a newly described freshwater fish, together with its congener Pseudobabus burchelli and an anabantid Sandelia capensis by assessing their scenopoetic and bionomic patterns. We found high habitat and isotope niche overlaps between the two redfins, rendering niche partitioning a less plausible sole mechanism that drives their coexistence. By comparison, environment–trait relationships revealed differences in species–environment relationships, making habitat filtering and functional equivalence less likely alternatives. Based on P. skeltoni's high habitat niche overlap with other species, and its large isotope niche width, we inferred the likelihood of differential resource utilization at trophic level as an alternative mechanism that distinguished it from its congener. In comparison, its congener P. burchelli appeared to have a relatively small trophic niche, suggesting that its trophic niche was more conserved despite being the most abundant species. By contrast, S. capensis was distinguished by occupying a higher trophic position and by having a trophic niche that had a low probability of overlapping onto those of redfins. Therefore, trophic niche partitioning appeared to influence the coexistence between S. capensis and redfins. This study suggests that coexistence of these fishes appears to be promoted by their differences in niche adaptation mechanisms that are probably shaped by historic evolutionary and ecological processes.     

Understanding thermostability in cytochrome P450 by combinatorial mutagenesis

The cytochromes P450 are an important class of mono-oxygenases involved in xenobiotic metabolism and steroid biosynthesis in a diverse set of life forms. Discovery of CYP-119, a P450 from the archea Sulfolobus solfataricus has provided a means for understanding nature's method of stabilizing this important protein superfamily. To identify classes of stabilizing interactions used by CYP-119, we have generated a randomized library of point mutants and screened for mutants that are less thermostable than the wild type by monitoring the characteristic Soret band in the visible region of the cell lysis. The selected mutants were characterized by differential scanning calorimetry to compare the temperatures of the melting transitions of the various mutants. The identified mutations suggested that electrostatic interactions involving salt links and charge-charge interactions, as well as contributions from other interactions such as aromatic stacking, and side chain volume of hydrophobic residues contribute to enhanced thermostability in this cytochrome P450.     

European springtime temperature synchronises ibex horn growth across the eastern Swiss Alps

Direct effects of climate change on animal physiology, and indirect impacts from disruption of seasonal synchrony and breakdown of trophic interactions are particularly severe in Arctic and Alpine ecosystems. Unravelling biotic from abiotic drivers, however, remains challenging because high‐resolution animal population data are often limited in space and time. Here, we show that variation in annual horn growth (an indirect proxy for individual performance) of 8043 male Alpine ibex (Capra ibex) over the past four decades is well synchronised among eight disjunct colonies in the eastern Swiss Alps. Elevated March to May temperatures, causing premature melting of Alpine snowcover, earlier plant phenology and subsequent improvement of ibex food resources, fuelled annual horn growth. These results reveal dependency of local trophic interactions on large‐scale climate dynamics, and provide evidence that declining herbivore performance is not a universal response to global warming even for high‐altitude populations that are also harvested.     

Trophic Assemblages of the Rocky Intertidal Zone in Vostok Bay,Sea of Japan

The ratios between the indices of relative abundance for different trophic life forms have been used to characterize bionomical types of a rocky intertidal zone. It has been shown that the distribution of life forms is determined by the geomorphological peculiarities of the surveyed intertidal areas. A brief critical historical review has been provided of the terms bionomy and bionomical type.     

Effects of zebra mussel attachment on the foraging behaviour of a larval dragonfly,Macromia illinoiensis

1. Larvae of Macromia illinoiensis Walsh are often colonised by the zebra mussel, Dreissena polymorpha Pallas, a recent invader to North America. To determine how mussel attachment affects an individual's foraging behaviour, we quantified capture of Hexagenia limbata Hexes mayfly prey and the distance moved by newly‐molted final instars before and after an individual's colonisation with zebra mussels. 2. In night trials, larvae sprawled above the sand, and caught more mayflies than individuals in daytime trials, but the estimated distance travelled did not differ. When resting under a layer of sand with only its eyes exposed during the day, an individual could capture a mayfly prey using a sit‐and‐wait ambush strategy. When sprawled above the sand, some larvae caught prey that rested on their legs. 3. When mussel‐free, individuals captured more prey than they did when carrying zebra mussels, although mussel attachment per se did not affect the estimated distance that a larva moved. 4. During day trials, but not night ones, the increasing mussel load of colonised individuals decreased prey capture and the distance moved in an apparent step‐wise function. Although the number of mussels carried did not differ, night foragers carried a heavier load. Independent of time of the day, the distance an individual travelled when mussel‐free was predictive of the number of prey it caught when colonised, suggesting that the greater general activity of some individuals helped mitigate negative effects that mussel attachment had on prey capture. 5. Our results add to a growing number of negative effects of zebra mussel colonisation on sprawling and hiding dragonfly larvae. Although the impact of these costs on dragonfly populations remains to be determined, a decrease in this guild of predators whose life cycle spans aquatic and terrestrial habitats might have cascading effects across ecosystems.     

Depth gradients in food‐web processes linking habitats in large lakes: Lake Superior as an exemplar ecosystem

相似文献   

Behavioural responses in three ichneumonid pollen beetle parasitoids to volatiles emitted from different phenological stages of oilseed rape

Pollen beetles (Meligethes spp.; Coleoptera: Nitiduliae) are a major pest of oilseed rape, Brassica napus L. (Brassicaceae) in northern Europe. Phradis interstitialis Thomson, P. morionellus Holmgr., and Tersilochus heterocerus Thomson (Hymenoptera: Ichneumonidae) are among the most frequent pollen beetle parasitoids. These three species differ in temporal occurrence, as well as in preferred host stage. The behavioural responses of female parasitoids to odours from oilseed rape at bud and flowering stage were evaluated in two‐choice experiments. The role of visual stimuli was examined by combining green and yellow colours with odour stimuli. All three species were attracted to odours from the bud stage of oilseed rape. Tersilochus heterocerus was attracted to odours of flowering rape, but the two Phradis species avoided the flower odours. However, when the odours of flowering rape were combined with yellow, and odours of the bud stage were combined with green, P. interstitialis was equally attracted to both stimuli, and T. heterocerus showed an increased preference for flower odours, while no effect of colours could be found in P. morionellus. The observed differences in responses between the parasitoids may reflect differences in their biology and may be involved in the niche segregation of these often coexisting species. The volatile blends released from the two phenological stages were identified and compared. Clearly, odours can be reliable cues for differentiating between oilseed rape in the bud and flowering stage. Of 20 identified compounds, 18 were released at a significantly higher rate from flowering plants. The terpenes sabinene, myrcene, limonene, and (E,E)‐α‐farnesene were the dominant volatiles in the bud and flower headspace. A group of aromatic compounds including benzaldehyde, methyl benzoate, and phenyl acetaldehyde were mainly released from flowering rape.